I. Field of the Invention
The present invention generally pertains to a relatively non-invasive plaque resolving device of the class adapted to be inserted through the lumen of a blood vessel and manipulated therethrough to a desired location to ply a cutting tool to excise deposits of atherosclerotic plaque from the internal surfaces of the vessel. More particularly, the present invention relates to a guidewire for use in conjunction with such a system.
II. Related Art
Impairment of the circulation of blood occasioned by intraarterial deposits of atherosclerotic plaque is a major symptom of cardiovascular disease. Obstruction of coronary arteries can lead to tissue death because of oxygen deprivation of heart muscle. Coronary infarction (heart attack) is the result. Plaque-induced stenosis of other major arteries can result in impairment of peripheral organ function. One long-used procedure for overcoming such obstructions and blockages involves a surgical by-pass operation in which the obstructed arteries are subtended by patient autographed blood vessels removed from other parts of the patient's body. Surgically invasive endarterectomy has also been used with limited success for clearing obstructed vessels.
The need has long existed for a less invasive and radical procedure to alleviate such blockages and achieve transmyocardial revascularization, or the like, in a manner which causes no significant damage to the healthy endothelial lining of the surrounding vessel. One technique that attempts to fulfill this need is balloon angioplasty in which an inflatable balloon is passed to the stenotic region of the affected artery and inflated with a fluid to a pressure (normally, about 5 atmospheres) to depress the plaque against the arterial wall thereby opening up the arterial volume. Because circulation is grossly impaired, however, balloon inflation/deflation must occur in a matter of seconds to avoid infarction. In addition, limited force is available because of the fear of damage to the arteries caused by overpressurization of the balloon. Also, the capture of plaque debris that may slough during the expansion process is not as yet provided for by such devices.
Other approaches include the use of a laser to clear obstructions in vessels as proposed, for example, in U.S. Pat. No. 4,207,874 to Choy. In that device, laser energy is conveyed by flexible fiberoptics in conjunction with a venial catheter and applied to the plaque obstruction in the occluded zone. In conjunction with this system various axial channels may be provided with appropriate fluid management manifolds in order to inject saline, aspirate debris with the saline and inject die for visualization. Additional coherently aligned fibers may be provided for actual viewing of the obstruction intraluminally. In addition to Choy, many other approaches utilizing variations on a laser excising system have also been proposed. Lasers, for example, have been utilized to resolve plaque by heating a catheter tip in a manner which causes the plaque tissue to, in effect, be melted away by the heated tip of the catheter resulting in permanent removal. The approach is illustrated by Hershenson in U.S. Pat. No. 4,748,979. A variety of cutting devices have also been proposed in conjunction with a catheter in which rotating cutters actually address and excise the stenosis. Most of these devices, however, appear to be ineffective for rapid cutting of the stenosis without affecting or damaging the relatively soft adjacent wall of the arterial vessel involved. U.S. Pat. No. 4,784,636 to Rydell is assigned to the same assignee as the present invention and illustrates such a device, an atherectomy catheter which includes a self-guiding catheter having an inflatable balloon disposed on the distal end portion thereof, the guide catheter being dimensioned to receive in its lumen an elongated drive tube having a rotational drive mechanism at its proximal end for rotating an angular cutting tip affixed to the distal end. In use, the guide catheter with the drive tube and cutter head retracted is advanced up to the occlusion, the balloon is inflated to lock the distal end in place and the cutter is rotated at high speed and advanced into the occlusion, while blood and any loose particular matter is aspirated. The balloon is then deflated and advanced further into the lesion and the steps repeated until the occlusion is removed.
A more recently issued patent to Rydell, common of assignee with the above invention, is U.S. Pat. No. 4,857,045, also directed to a self-guiding atherectomy catheter system, utilizes a coaxial system of inner and outer flexible tubular members in which the inner tubular member is journaled for rotation at the distal end of the outer tubular member. A motor located at the proximal end of the catheter assembly drives the inner tubular member including a dome-shaped rotational cutting head containing a number of substantially round open ports for addressing blockage material upon rotation which is fixed to the inner tubular member just beyond the end portion of the outer tubular member. Aspiration is accomplished through the inner tubular member and a flushing fluid such as saline administered through the outer tubular member, as required.
While the last-discussed system represents an improvement with regard to centering and operating the atherectomy catheter within the vessel of interest, there remains a need to improve the efficacy of such devices with respect to complete stenosis removal. There also exists a need to improve the ability of the operator to guide the catheter in navigating the vascular system particularly with regard to precise positioning of the cutter at the situs of the occlusion of interest. Positioning the cutter with respect to the blockage about the periphery of the vessel is difficult to achieve without a controlling guidewire. Guidewires have been used with success in several types of over-the-wire catheter systems but heretofore they have not been used with rotating atherectomy devices because of the need to coordinate the guidewire placement to avoid the cutter head.
Of particular interest is the so-called Monorail.TM. catheter which has been used in connection with angioplasty balloon catheters with great success. In that system only a small distal segment of the balloon catheter actually passes over the guidewire with the remaining portion of the guidewire then extending generally along the exterior wall external to the catheter in the proximal direction. The short segment at the distal end provides the necessary control. The Monorail.TM. catheter and its use is more particularly described in the Bonzel U.S. Pat. No. 4,762,129.
With respect to the present invention, there remains a need to provide more precise positioning of an atherectomy catheter within the vessel of interest to assure proper and complete removal of the occlusion. This is true not only for navigating the catheter along the vessel but also for proper positioning of the cutter with respect to the material to be removed.